1. Field of the Invention
This invention pertains generally to using tires as a source of supplemental fuel to heat a rotating kiln, and more particularly to a feed chute apparatus for injecting tires and other combustible materials into the kiln.
2. Description of the Background Art
Rotating kilns are frequently used in the production of cement. Because such kilns operate at extremely high temperatures, it is possible to burn various forms of liquid and solid combustible waste materials as a source of supplemental heat. At the high temperatures found in such kilns, which are on the order of 3400 degrees F. and above, the waste materials tend to combust fairly completely while producing little or no undesirable gaseous or solid emissions. Therefore, these waste materials can serve as a supplemental fuel, thereby reducing the demand for and cost of the primary fuel.
One form of waste that is burned in cement kilns is rubber tires from automobiles and trucks. Rubber tires make a very good source of supplemental fuel for a rotary kiln because they burn at comparatively hot temperatures. The extremely high temperatures within a cement kiln will cause the rubber tires to burn without any significant liquid, solid or gaseous waste byproducts which might otherwise be detrimental to the environment. Accordingly, the burning of tires in rotary kilns helps alleviate the growing problem of tire disposal without significantly impairing the environment.
Conventional feed systems used for injecting tires into a cement kiln have typically suffered from several deficiencies. For example, some feed systems require that the tires be shredded and then packaged into “fuel packages” of a specific size to accommodate the dimensions of the feed system. However, such processing of used tires increases the overall cost of tire disposal, increases the cost of operating the kiln, as well as requires the use of special equipment and additional manpower to cut the tires and package the resulting pieces into suitably sized packages. Therefore, it is more efficient and cost effective to inject whole tires into the kiln.
One known method of tire injection into the kiln uses gravity to drop a tire into an opening in the kiln wall from a loading area as the kiln rotates. The loading area may be positioned vertically or rotates with the kiln and gravity causes the tire or other fuel item to slide into the interior area of the kiln when the loading area becomes disposed substantially vertically. A drawback of that type of system, however, is that the tire is dropped from the top of the kiln into highly fluidized material causing the material to splash and thereby creating excessive turbulence and inconsistent combustion within the kiln. To address that problem, feed systems have been developed that will positively inject the tire into the kiln during a portion of the rotational travel of the kiln without relying on gravity to do so.
For example, one known injection system comprises an entrance chute having an outer end portion protruding outwardly from a wall of the kiln and an inner end portion which protrudes into the kiln. The entrance chute further is disposed such that it is positioned tangentially to the kiln wall. The entrance chute includes a gate assembly having a cam follower assembly and a pivotally mounted gate member. The cam follower assembly causes the gate member to be urged pivotally between open and closed positions in response to movement of the cam follower assembly over a cylindrical camming wall positioned at a predetermined location relative to the kiln. When the cam follower assembly has caused the gate member to open, a plurality of tires or other items forming a source of supplemental fuel are positively propelled into the entrance chute by one or more external tire injecting apparatuses synchronized in operation to rotation of the kiln. A dam formed at the inner end portion of the entrance chute prevents highly fluidized material within the kiln from flowing up into the entrance chute and further forms a channel relatively free of the fluidized material into which the tires may be injected during a predetermined portion, or portions, of rotational travel of the kiln.
However, even the positive injection system described above has drawbacks, namely complexity and cost. Therefore, a need still exits for an efficient, low cost feed system for injecting tires into a rotating kiln. The gravity feed system of the present invention satisfies that need, while overcoming deficiencies found in conventional feed systems.